Nervousness/random

I’m always getting so nervous that my baby isn’t alive. I just hit 15 weeks today and I haven’t had an ultrasound for awhile.. and I don’t go back till January 25th. I’m freaking out because I feel like that is such a long time ! How do I know everything is okay? A couple days ago I was getting bad cramps and even to my backside. But it was only one day. I don’t want to stress myself out too bad but I don’t know what to do. Anyone have any opinions ? 😭